Spark ignition system



Se t. 3, 1968 G 3,399,658

SPARK IGNITION SYSTEM F'iled April 26, 1966 IIJ wm T1U/ U BH E ml D FLUDISTRIBUTO 3,399658 SPARK IGNITION SYSTEM Brian Gilbert, SuttonColdtield, England, assignor to Joseph Lucas (Industries) Limited,Birmingham, England, a British company Filed Apr. 26, 1966, Ser. No.545,405 Claims priority, application Great Britain, May 5, 1965,18,904/65 3 Claims. (Cl. 123148) ABSTRACT OF THE DISCLOSURE In a sparkignition system, current flow in a winding is interrupted by asemi-conductor switch, and the energy available as a result of theinterruption is used to produce a spark. A feedback transformer is usedto turn the switch oi rapidly, and in addition, a capacitor is proviedwhich maintains the current flow in the winding until the switch isfully olf.

This invention relates to spark ignition systems for internal combustionengines.

A spark ignition system according to the invention comprises incombination a switch which can be turned on and off by signals appliedto a control electrode forming part of the switch, means for applyingsignals to said control electrode to turn the switch on and ofl andthereby produce the required sparks, a transformer having a primarywinding in series with said switch, and a secondary winding coupled tosaid triggering electrode, said transformer increasing the drive to saidtriggering electrode when the switch is turned off and so reducing thetime taken to turn the said switch otf, and a capacitor connected incircuit with said switch in such a position that when the switch startsto turn otf current flowing through the switch is diverted through thecapactor untl the capacitor is charged, the position of said capacitorbeing such that it does not dissipate energy stored in said primarywinding.

In the accompanying drawings, FIGURES 1 and 2 are circuit diagramsillustrating two examples of the invention.

Referring to FIG.URE 1, there are provided terminals 11, 12 which in useare connected to the battery of a vehicle so as to be positive andnegative, Conveniently, the positive terminal is earthed as indicated.Connected in series between the terminals 11, 12 is an engine-driveninterrupter 13, a resistor 14, and an inductor 15. The interrupter 13 isbridged by a capacitor 16, and a point intermediate the resistor 14 andinductor 15 is connected to the terminal 12 through parallel pathscontaining respectively a capacitor 17 and a resistor 18, and is alsoconnected through the secondary winding 19 of a transformer 21 to thegate of a gate controlled switch 22. The winding 19 is bridged by aresistor 23.

The switch 22 is a device havng properties similar to a controlledrectifier, plus the additional property that it can be switched oif by anegative signal between its gate and cathode. The device 22 has itscathode con nected to the terminal 12, and its anode connectedto theterminal 11 through a series circuit including the primary winding 20 ofthe transformer 21, the primary winding 24 of an ignition transformer25, and a resistor 26. The winding 20 and switch 22 are bridged by acapacitor 27, and the secondary winding 28 of the transformer 25 is connected through a distributor 29 to the plugs 30 of the engine in turn.

In operation, when the interrupter 13 closes, current flows through theinterrupter 13, the resistor 14, the winding 19 and resistor 23 inparallel, and the gate and cathode of the switch 22 to turn the switch22 on. Curnited States Patent C) rent can flow through the switch 22,the winding 20, the winding 24 and the resistor 26. At the same time,current flowing through the resistor 14 flows through the inductor 15,so that energy is being stored in the inductor 15 and the windings 20and 24. When the interrupter 13 opens, the energy stored in the inductor15 causes the gate of the switch 22 to become negative with respect tothe cathode of the switch 22 and after a short delay due to the chargestorage efiect of the switch 22, the switch 22 starts to turn 0. As theswitch 22 starts to turn ot, current flowing in the winding 20decreases, but the current flowing in the winding 24 does not decreaseimmediately because of the presence of the capactor 27. However, thefalling current in the winding 20 causes energy to be fed back to thegate of the switch 22 by way of the winding 19, and this additionalenergy assists in turning oi the switch 22. Thus, the switch 22 turns orapidly, and the rapid fall in current in the winding 24 produces aspark at the appropriate plug. It should be noted that the pointintermediate the resistor 14 and inductor 15 is driven negative by theinductor 15, but is driven positive by the transformer 21. Thus, largechanges of voltage do not occur at this point, which is of considerableassistance where the interrupter 13 is of limited voltage rating. Itwill be appreciated that the interrupter 13 could be replaced by manyother forms of engine-driven switch which need not be mechanical.

The purpose of the resistors 18, 23 is to minimize or preventoscillations in the circuit including the gate of the switch 22. Thecapacitors 16, 17 limit the rate of rise of voltage across thenterrupter 13, thereby minimising arcing. The capacitor 27 in additionto its function already described, limits the voltage across the switch22 to an acceptable value.

It should be noted that with the capacitor 27 connected as shown, fallof current in the winding 24 is delayed when the switch 22 starts toturn ofr without dissipation of the energy stored in the winding 20. Thesame eect can be achieved by having one side of the capacitor 27connected to a point intermediate the windings 20, 24 and its other endconnected to the terminal 11 either directly or through the resistor 26.However, the capacitor 27 must not be connected directly across theanode and cathode of the switch 22, otherwise it dissipates energystored in the winding 20. In a modification, a resistor is connected inseries with the capacitor 27 in order to protect the switch 22 in theevent of it being switched on accidentally whilst the capacitor 27 ischarged to a high voltage. In another modification, the inductor 15 isnot coupled to the gate circuit as indicated, but forms the primarywinding of a transformer the secondary winding of which is coupled tothe gate circuit in the same way as the inductor 15. This modificationis particularly useful in negative earth systems.

Tuming now to the exarnple shown in FIGURE 2, the connections betweenthe supply terminals 11, 12 and the gate of the switch 22 are the sameas those shown in FIGURE 1, and are designated by the same referencenumerals. Moreover, the cathode of the switch 22 is con nected to theterminal 12, and the anode of the switch 22 is connected to one end ofthe winding 20 as before. However, the other end of the winding 20 isconnected to the terminal 11 through a diode 31, an inductor 32 and aresistor 33 in series. A point intermediate the winding 20 in FIGURE 1.However, the way in which the sparlgs are produced is somewh'atdifferent, In order to understand the operation, assume thatthecapacitor 34 is charged and the switch 22 is turned off. At theinstant when the switch 22 is turned on, the capacitor 34 dischargesthrough the winding 24 and the switch 22 and winding 20 to produce therequired spark. At the same time, current flo'ws through the seriescircuit ncluding resistof33, inductor 32, diode 31, winding 20 andswitch 22, so that energy is stored in inductor 32. When the switch 22is turned ofi, the energy stored in inductor 32 is transferred to thecapacitor 34, the winding 24 being bridged by the diode 35 while thecapacitor 34 is being charged. The cycle is then rpeated to produce thenext spark. It will be appre- Ciated that the transformer 21 assists inturning the switch 22 oif as in FIGURE 1, andthat the capacitor 34 ischarged to a voltage considerably in excess of the battery voltage. Thecapacitor 34 aiso perforrns the function of the capacitor 27 in FIGURE1, in that it maintains current flow in the winding 32 until the switch22 is fully off, whereupon the stored energy is transferred to capacitorIn both FIGURE 1 and FIGURE 2, the transformer 21 assists in turning onthe switch 22 rapidly as well as switching it oi. In FIGURE 1 thiseffect is not important, but it is of assistance in FIGURE 2, becausethe spark is produced when the switch 22 is turned on. Althoughin FIGURE2 the spark is not produced when the switch 22 is turned oif, it isstill of importance that the switch 22 should be turned off rapidly, sothat maximum energy is transferred from the inductor 32 to the capacitor34, with a minimum of dissipation in switch 22.

In both examples, the switch 22 could be replaced by other forms ofswitch the conduction of which can be contro1ied by signals applied to acontrol eiectrode. For example, the switch 22 could be replaced by atransistor. A transistor does not of course require a bias to turn itoif, it being only necessary to remove the bias which turns thetransistor on. However, for rapid switching, it is preferable not torely merely on removai of a bias from the base of a transistor, but toprovide a definite signal to bias the transistor to nonconduction. Thecircuit components would of course be chosen to provide a bias to thetransistor as long as the transistor is required to conduet.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. 1 spa rlg ignition system for an internal cornbustion engine,comprising in combination a D.C. source, a series circuit connectedacross said D.C. source and including a storage winding, the prirnarywinding of a feedback transformer and a semi-conductor switch which canbe turned on and otf by.signais applied to a controi elec trede formingpart of the switch, means operable in timed relationshipto the enginefor applying signals to said control electrode to turn said switch onand to turn said switch off,a secondry winding on said feedbacktransforrner, mens coupling said secondary winding to said controlelectrode whereby said feedback transformer assists rapid turn-oi ofsaid switch, a capacitor, means coupling said capacitor in the circuitwhereby said capacitor maintains current flow in said storage windingwhen said switch starts to turn otf untilsaidswitch is fnlly off, saidcapacitor having no effect on said feedback transformer but ensuringthat current flow in said storage winding is interrupted rapidly, andmeansutilising the energy available when the current flow in saidstorage winding is interrupted to produce sparks at the p1ugs of theengine in turn in timed relationship to the engine.

2. A system as ciaimed in claim 1 including an ignition transformerhaving a secondry winding coupled to said piugs in turn through adistributor and a primary winding constituted by said storage winding,each spark being produced when the switch is fully turned off.

3. A system asc1airned in claim 1 including a diode in said seriescircuit positioned between said storage winding and said prirnarywinding, said capacitor being connected across the series circuit ofsaid primary winding and said switch in series with the primary windingof an ignition transformer the secondary winding of which is connectedto the plugs of the engine in turn through a distributor, the energystorcd in the storage inductor being transferred to the capacitor whensaid switch is fully ofi and being retained by said diode, and eachspark being produced by discharge of the capacitor when said switch isturned on.

References Cited UNITED STATES PATENTS 7/ 1966 Stuermer. 1/1967 Quinn.

RALPH BLAKESLEE, Prmary Examiner.

